The biofuel industry employs yeast to covert sugars into ethanol. A problem in the industry is that fermentation process equipment and/or the mash can become contaminated with bacteria that reduce production yields. As a result, the efficiency of such ethanol fermentation is significantly limited by other micro-organisms contaminating the process, including for example lactic acid and acetic acid bacteria (e.g. yield loss bacterium). Such contaminating bacteria complete for sugar supply with the yeast, resulting in a decrease in ethanol production. In addition, the contaminating bacteria can decrease the pH conditions which further inhibit the growth of ethanol-producing yeast. Lactobacillus and Acetobacter are well-known yield loss bacterium in the ethanol fermentation industry. As a result, there is a need for preventing ethanol fermentation yield loss from bacterial infection introduced in ethanol fermentation procedures.
Antibiotics are commonly used as a means for controlling unwanted yield loss bacterium in fermentation plants. However, the byproducts of corn ethanol fermentation, including distiller's wet grain solids (i.e. wetcake byproduct) are often used for feed supplies. For example, distiller's grain and dried yeast are frequently used for beef and dairy cattle feed. The conventional use of antibiotics, such as virginiamycin, in the ethanol fermentation methods for controlling yield loss undesirably results in the incidental (i.e. sub-therapeutic) dosing of antibiotics to such animals. Data confirms the survival of antibiotics through the distillation process at low levels into the byproducts. There is significant public opposition to such incidental antibiotic dosing into animal feed supplies, as well as suggested regulatory (Food and Drug Administration) consideration for the banning of the use of antibiotics in the ethanol industry. In addition, the use of antibiotics is costly. Therefore, there is a clear desire to eliminate the use of such antibiotics from the corn ethanol fermentation process.
Antibiotic alternatives have included oxidizing biocides, such as stabilized chlorine dioxide, which may be pumped into a fermenter prior to the fermentable substrate being loaded. During the course of fermentation, the organic acids produced by contaminating bacteria are thought to activate the chlorine dioxide in the vicinity of the bacterial cells. Chlorine dioxide has also been used for disinfecting process pipes and heat exchangers. Other antibiotic alternatives that have been employed in limited fashion include inorganic oxidizers, such as hydrogen peroxide or urea hydrogen peroxide.
A chemical alternative to antibiotics for use in the biofuel industry includes peracids. Peracids are known for use as sanitizers, disinfectants, deodorizers, and bleaching agents, among other uses. Peracids are particularly well suited for use in both clean-in-place systems (CIP) and clean-out-of-place systems (COP), as well as industrial uses including antimicrobial control for washing or processing meat surfaces, vegetable fume applications, food and beverage applications and the like. See U.S. Pat. Nos. 7,498,051, 7,504 123, 7,507,429, and 7,569,232, which are herein incorporated by reference in their entirety. However, such CIP and/or COP methods have not reportedly been used in the fermentation industry. Accordingly, it is an objective of the claimed invention to develop methods, compositions and systems for improved cleaning and sanitation procedures using peracids for use in ethanol fermentation processes.
A further object of the invention is to develop methods, compositions and systems for improved ethanol yield in ethanol fermentation processes through the elimination of unwanted bacterial infiltration.
A further object of the invention is an improved yield loss control for ethanol fermentation to replace the convention use of antibiotics in the field.